Please note that the content of this book primarily consists of articles available from Wikipedia or other free sources online. A rare disease, commonly known as orphan disease, is any disease occurring in a small percentage of the world population, appearing early in life, usually because of a genetic defect. Though with a very low prevalence, medical evidence indicates that there could be between 5,000 and 8,000 known rare diseases worldwide, the most well-known being cystic fibrosis, elephantiasis, progeria, werewolf syndrome, albinism and others, affecting 5 per 10,000 persons in Europe and 1 in 10 Americans. Despite of the lack of any efficient treatment for such types of diseases, according to medical studies, in the past 10 years, researchers found nearly 1,150 orphan drugs, developed specifically to treat these rare conditions, however, only around 150 have been approved. To find out more about rare diseases, their prevalence and treatment availability – read this book.